* Repo collab now supports basic default roles developer/user/guest like
project collab does
* User/Anon collab for repos and projects are now stored as fields instead of
in dedicated tables, there was never a need for dedicated tables but I didn't
see that before
* Repo push op is now part of `ProjectOperation`
* `RepoRole` and related code has been entirely removed, only project roles
remain and they're used for both repos and projects
* This is the first not-totally-trivial DB migration in Vervis, it's automatic
but please be careful and report errors
